Coexpression of Kir2.1 and TeNT-LC in callosal neurons caused more severe defects in the development of callosal projections in the somatosensory cortex than those of individual transfections at P9. A–D , Kir2.1/TeNT-LC-coexpressing callosal axons were more dramatically reduced in both S1 and the S1/S2 border region ( D ) compared with control ( A ), Kir2.1 ( B ), and TeNT-LC ( C ) axons. It should be noted that these reduced callosal axons in S1 bypassed layers II–III and ended in layer I ( D , H ). The S1 regions in A–D were enlarged in E–H , respectively. The S1/S2 border regions in A–D were enlarged in I–L , respectively. Scale bars: A–D , 350 μm; E–L , 100 μm. Con, Control; K+T, Kir2.1 plus TeNT-LC.